Integrated circuit device fabrication by plasma etching

Abstract

A trench etching process is disclosed in which a substrate is etched under conditions that promote forward sputtering of mask material in a plasma reactor having at least three electrodes. The forward sputtering impedes etching of trench sidewalls by depositing a protective layer of mask material on the sidewalls of a trench being formed. By controlling the amount of forward sputtering, one can control the trench profile and aspect ratio (depth to width). By employing forward sputter etching in a three or more electrode reactor, trenches of less than one micron in width and having aspect ratios of at least 2.5:1 are formed. Such trenches are used in trench capacitors of high density DRAMs. A disclosed plasma reactor includes a grounded first electrode which forms part of the reactor's enclosure, a coiled second electrode disposed above and separated from the reactor enclosure by a dielectric shield, and a planar third electrode located below the substrate to be etched. A plasma is generated by providing radio frequency energy from the second electrode to the enclosure interior. The charged species from that plasma are directed to the substrate by applying a bias between the first and third electrodes.

What is claimed is: 
     
       1. A method of etching a trench in a substrate having a top surface, the method comprising the following steps: supporting said substrate within an enclosure; and   plasma etching selected portions of said substrate under defined etch conditions such that material from the top surface of the substrate is forward sputtered to induce deposition on sidewalls of said trench during etching,   wherein a first electrode includes a coil electrically coupled to a radio frequency power source such that by inductive coupling a plasma is generated about the substrate by applying a potential between a first and a second electrode, and wherein charged species are directed from said plasma onto said substrate by applying a potential to a third electrode.   
     
     
       2. The method of claim 1 wherein the material from the top surface of the substrate includes an oxide, a nitride, a silicate glass, or a combination thereof. 
     
     
       3. The method of claim 1 wherein the substrate is supported in a defined plane, and wherein the first electrode is oriented substantially perpendicular to said defined plane, and the second electrode is located above the substrate and is oriented substantially parallel to said defined plane, with the potential being produced by a radio frequency signal in the second electrode, and   wherein the third electrode is located beneath the substrate and is oriented substantially parallel with the defined plane.   
     
     
       4. The method of claim 1 wherein the step of plasma etching includes the following steps: introducing a gas of defined composition chosen to promote forward sputtering of the material from the top surface of the substrate;   producing the plasma within said enclosure by applying a potential between said first and second electrodes; and   directing said plasma onto said substrate under said defined etch conditions such that material from the top surface of the substrate is forward sputtered to induce deposition on sidewalls of said trench during etching, wherein the one or more gases are provided at the substrate surface while said plasma is being produced.   
     
     
       5. The method of claim 4 wherein the defined composition of the gas changes during the step of plasma etching. 
     
     
       6. The method of claim 5 wherein the substrate is silicon and wherein a first gas composition is supplied initially in the step of plasma etching, and said first gas composition is chosen to remove a native oxide on exposed portions of the silicon substrate. 
     
     
       7. The method of claim 6 wherein the first gas composition is boron trichloride. 
     
     
       8. The method of claim 5 wherein the substrate is silicon and wherein a second gas composition is supplied after the first gas composition in the step of plasma etching, and wherein the second gas composition is chosen to substantially promote forward sputtering of the material from the top surface of the substrate. 
     
     
       9. The method of claim 8 wherein the second gas composition includes primarily HCl or HBr. 
     
     
       10. The method of claim 1 wherein the trench formed by said method has (i) a sub-micron primary dimension on the top surface of said substrate, and (ii) an aspect ratio of at least 2.5:1, said aspect ratio representing the ratio of the trench's depth in the substrate to the trench's primary dimension on the top surface of the substrate. 
     
     
       11. The method of claim 10 further comprising steps of forming complete devices on the substrate such that an integrated circuit is formed. 
     
     
       12. A method of etching a trench in a substrate having a top surface covered by a patterned hard mask, the method comprising the following steps: supporting said substrate within an enclosure; and   plasma etching selected portions of said substrate under defined etch conditions such that material of the patterned hard mask is forward sputtered to induce deposition on sidewalls of said trench during etching,   wherein a first electrode includes a coil electrically coupled to a radio frequency power source such that by inductive coupling a plasma is generated about the substrate by applying a potential between a first and a second electrode, and wherein charged species are directed from said plasma onto said substrate by applying a potential to a third electrode.   
     
     
       13. The method of claim 12 wherein the hard mask includes an oxide, a nitride, a silicate glass, or a combination thereof. 
     
     
       14. The method of claim 12 wherein the substrate is supported in a defined plane, and wherein the first electrode is oriented substantially perpendicular to said defined plane, and the second electrode is located above the substrate and is oriented substantially parallel to said defined plane, with the potential being produced by a radio frequency signal in the second electrode, and   wherein the third electrode is located beneath the substrate and is oriented substantially parallel with the defined plane.   
     
     
       15. The method of claim 12 wherein the step of plasma etching includes the following steps: introducing a gas of defined composition chosen to promote forward sputtering of the hard mask material;   producing the plasma within said enclosure by applying a potential between said first and second electrodes; and   directing said plasma onto said substrate under said defined etch conditions such that material of the patterned hard mask is forward sputtered to induce deposition on sidewalls of said trench during etching, wherein the one or more gases are provided at the substrate surface while said plasma is being produced.   
     
     
       16. The method of claim 15 wherein the substrate is silicon, the hard mask material includes a silicon oxide, and the one or more gases introduced into the enclosure include HCl, HBr, SiCl 4 , or a combination thereof. 
     
     
       17. The method of claim 15 wherein said defined etch conditions change during the step of plasma processing. 
     
     
       18. The method of claim 15 wherein the defined composition of the gas changes during the step of plasma etching. 
     
     
       19. The method of claim 18 wherein the substrate is silicon and wherein a first gas composition is supplied initially in the step of plasma etching, and said first gas composition is chosen to remove a native oxide on exposed portions of the silicon substrate. 
     
     
       20. The method of claim 19 wherein the first gas composition is boron trichloride. 
     
     
       21. The method of claim 18 wherein the substrate is silicon and wherein a second gas composition is supplied after the first gas composition in the step of plasma etching, and wherein the second gas composition is chosen to substantially promote forward sputtering of the hard mask material. 
     
     
       22. The method of claim 21 wherein the second gas composition includes primarily HCl or HBr. 
     
     
       23. The method of claim 22 wherein the second gas composition further includes one or more of the following gases: nitrogen, argon, silicon tetrachloride, carbon monoxide, and carbon dioxide. 
     
     
       24. The method of claim 12 wherein the trench formed by said method has (i) a sub-micron primary dimension on the top surface of said substrate, and (ii) an aspect ratio of at least 2.5:1, said aspect ratio representing the ratio of the trench's depth in the substrate to the trench's primary dimension on the top surface of the substrate. 
     
     
       25. The method of claim 24 further comprising steps of forming complete devices on the substrate such that an integrated circuit is formed.